In the production of extruded materials whereby such materials as ceramics, polymers, gels etc. are extruded into sections, it is often extremely critical that the sections be of identical or substantially identical size and shape. In the catalyst industry, for example, gels of silica, alumina etc. are extruded into sections which are to be packed tightly into columns etc. In many instances, the efficiency of the particular process which employs the catalyst bed, is totally dependent upon the catalyst. In such procedures, often times the mere packing of the catalyst means the difference between whether the process is a raving success or another "me too" system.
Successful packing of a column, etc., with a catalyst among other requirements, depends somewhat upon the shape and size of the catalyst particles, i.e. the more identical, the better the packing. In the past, many attempts have been made to devise apparatuses, systems and procedures for producing extrudate sections of substantially identical shape and size. For example, the industry has experienced the use of cutting knives which slice the extrudate from the extruder die plate as it emerges. However, since the pressure in the extruder is not uniform over the entire surface area of the die plate due to the worm screw therein, the extrudate is more rapidly extruded at the center of the die plate than at its peripheral edges. The extrudate sections are therefore not of uniform length. Cutting wires are also inadequate for the same reason.
One of the most widely used methods of cutting extrudates comprises extending material into a rapidly spinning disc. The rotary motion of the disc, when it is hit by the extrudate, causes breakage of the extrudate at the point where it emerges from the die. This type of cutter, however, also fails to produce sections of extrudate of even length if it is about the same size or slightly larger than the die plate in diameter, because the rotating disc travels faster at its outer edge than at its center. It therefore causes the extrudate to break at a different place along its length at the outside edge than at the center of the disc. If the disc is greatly enlarged so as to enable the extrusion of the material into an area thereof which is traveling about the same speed across its diameter, substantially identical lengths of extrudate are produced but the disc must be so large so as to render it cumbersome. Furthermore, disc type cutters cannot practically be attached to extruders in such a manner so as to allow facile replacement and/or cleaning of the die plate without complete removal of the cutter. Disc cutters also spray the extrudate sections in a random manner so that they collide and become damaged or adhere to one another and otherwise are rendered less useful.